The present invention broadly relates to machine drives and, more specifically, pertains to a new and improved construction of an orbital drive for a machine table.
Generally speaking, the drive of the present invention is a drive fo a machine for the manufacture of an electrode-workpiece by means of a form grinding tool of a similar spatial shape, which drive generates the orbital movement necessary for an abrading or grinding operation between the form grinding tool and the electrode-workpiece and changes the eccentricity of such orbital movement.
In other words, the drive means of the present invention is for generating between a blank for an electrode-workpiece having a first spatial configuration and a form-operating tool having a second spatial configuration similar to said first spatial configuration a relative orbital motion requisite for fabricating the electrode-workpiece from the blank by an abrading operation in an abrading machine and for altering a predetermined degree of an eccentricity of the relative orbital motion and comprises at least one motion-generating means for generating the relative orbital motion.
The construction of moulds encompasses the manufacture of moulds for pressure casting, injection molding, punching, hot forming, cold forming, and forging of materials formed of steel or other metals, plastics, and rubber as well as their respective alloys and mixtures. These moulds are frequently complicated and exhibit a three-dimensional construction. The aircraft and automobile industries especially require such type of difficult-to-manufacture forms or moulds which must be manufactured to very close tolerances. By the same method, there are also fabricated tools or construction parts (e.g. in the engine industry) of difficult to machine materials (e.g. high temperature alloys). Such moulds or complex three-dimensional parts such as engine parts are manufactured by spark erosion or electrochemical machines. The electrodes used for this purpose have the same complicated three-dimensional surface as the respective moulds or parts to be manufactured. During the course of the most recent developments, such electrodes have been manufactured on special machines. The manufacture occurs in a manner such that the electrodes are made from the solid material by means of a grinding or abrading operation or a filing operation. The material, could for instance, be graphite. The tool required for this purpose already has substantially the shape of the electrode with an over-dimensional allowance. The grinding or abrading operation or filing operation is accomplished due to a relative movement between the tool and the electrode that is to be machined from the solid piece. A grinding or abrading agent is introduced on to the surface of the tool to support the grinding or filing operation, or the tool already has a rough surface (steel with an eroded surface). Further, a fluid is introduced into the gap between the tool and the workpiece.
The relative movement is composed of two types of movement. The one type is a feed movement of the grinding or filing tool toward or away from the electrode-workpiece (usually vertical). This feed movement can also be circular (usually vertical). The other type is a circular movement of the electrode-workpiece in the horizontal plane, i.e. in a plane substantially perpendicular to the direction of the feed movement. This circular movement can also be termed orbital or planetary movement, and it can be also be spherical
The radius, respectively the eccentricity, of the circular movement can be adjusted. The grinding or abrading operation is carried out until the electrode-workpiece assumes a spatial shape similar to the tool. Then the relative movements are stopped. This is achieved by a gauge, also termed depth gauge, mounted on the machine. The spatial shape of the electrode-workpiece can be made larger or smaller than the spatial shape of the tool. This is accomplished by setting the desired eccentricity of the circular or orbital movement. This known manner of manufacture of the spatial shape of the electrodes has the following disadvantages:
The eccentricity of the relative circular or orbital movement cannot be altered during the grinding or abrading operation. For this purpose the machine must be stopped.
The setting of the eccentricity is not accurately accomplished. This is so because the eccentricity has to be set at two locations of the workpiece support successively and independently of one another. Despite great care on the part of the operator, a certain amount of play cannot be avoided, so that the setting of the eccentricity at the second point will differ from that at the first point.